Note: Descriptions are shown in the official language in which they were submitted.
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PRODUCTION OF FAMILIAL, NON-MODULAR, PLURAL COLOUR
PATTERNS ON A MOVING SUBSTRATE.
TECHNICAL FIELD
This invention relates to the continuous application of liquid or semi-
liquid paint coatings to a moving substrate.
The invention was devised primarily for the application of coatings of
paint to metal strip, for example steel strip coated with a corrosion
resistant
metallic alloy, and is described primarily in that context hereinafter.
However
it will be apparent that it is applicable to the application of paint coatings
to
substrates of other materials, provided the substrate is substantially
impervious
to the coating and, at least in preferred embodiments of the invention, is
capable
of being heated to above the glass transition temperature of a solid paint
composition to be applied to the substrate.
BACKGROUND ART
The application of paint to steel strip in large scale, continuously
operating, steel finishing mills is a highly developed art.
Typically, the substrate strip is progressed through a coating station
wherein liquid paint, comprising pigments and other paint solids dissolved in
a
solvent or otherwise dispersed in a liquid carrier, is applied to the
substrate by
a dipping, spraying, roller coating or like process for applying a liquid film
to
the substrate, which film is subsequently allowed or caused to evaporate to
leave
a solid paint coat on the substrate.
It is also known to apply paint composition to a heated substrate wherein
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the paint is applied as a liquid melted from a solid body of substantially
solvent
free paint composition by contact of the body with, or near approach of the
body to, the hot substrate. In this context the term "liquid" includes high
viscosity liquids, that may approach soft, plastic solids in nature, as well
as
easily flowing liquids.
That last mentioned mode of depositing liquid material on a substrate is
referred to as "melt deposition" and the deposited liquid is referred to as a
"melt
deposit" hereinafter.
Previously the deposition rate of melt deposits was determined by
controlling the contact pressure between the solid paint body and the
substrate,
while maintaining constant all of the many other parameters affecting the
deposition rate. Such a process is described in US patent No. 3,630,802 to
Dettling.
The difficulty of accurately controlling all of those parameters makes it
difficult to obtain constant deposition rates of low value when using Dettling
type pressure controlled melt deposition processes. This lead to their
replacement, in painting operations, by the melt deposition technique
described
in our Australian patent No. 667716.
Briefly stated, that Australian patent discloses depositing a polymer based
coating composition onto a side of a substrate metal strip moving at a
constant
speed, by heating the strip to a temperature above the glass transition
temperature of the composition, and driving a solid block of the composition
towards the strip at a predetermined block speed.
It is then only necessary to control the block speed to cause a melt
deposit to be applied to the strip at a precisely controlled deposition rate,
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without the need to closely control other operating parameters, in that each
of
those other parameters need only lie within a broad range of working values.
As is also disclosed in that Australian patent, the melt deposit may then
be spread over the surface of the strip by a pressure roll to emerge as a
smooth,
wet coating on the strip.
Irrespective of the mode of deposition, the prior art has been restricted
to the production of mono-chrome product, wherein a uniform coating is
applied to the whole of at least one side of the substrate strip.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide ornamental, plural colour
paint coatings, wherein the differently coloured components of the coating are
applied during a single pass of a substrate through a painting station.
It is well known that some patterns displaying random variation, in the
sense that no repeating module of the pattern may be discerned, may,
nevertheless, be seen as being members of a family of related patterns, in the
sense that individual expressions of the randomly variable patterns of one
family
have a recognisable family similarity, enabling them to be readily
distinguished,
by eye, from individual expressions of the randomly variable patterns of other
families.
Wood grain patterns may be cited as typical examples of patterns of the
kind referred to in the preceding paragraph. One has no difficulty in
distinguishing between veneers of, for example the four "families" of teak,
pine,
mahogany, and silky oak, although no two pieces of veneer of any one timber
are identical.
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Such randomly variable patterns maintaining a family resemblance are
referred to as "familial, non-modular patterns" hereinafter.
The concept of familial, non-modular patterns is of significance to the
present invention. If, for example, a domestic appliance has a cabinet made of
panels of plural coloured, painted sheet steel, it is desirable that there be
no
discernible repetition of the pattern in any one panel or from panel to panel
of
the appliance, but it is also desirable that each panel bears a strong family
resemblance to the others.
Thus, another object of the present invention is to provide for the
continuous application of a paint coat displaying a familial, non-modular,
colour
pattern to a substrate, during a single pass of the substrate through a
painting
station.
Still another object is to provide for the reproducibility of the family
likeness of familial coatings produced by painting operations that may be
spaced
apart in time.
Meeting that last objective enables a steel finisher, for example, to accept
orders for painted strip identified by reference to a familial, non-modular
coating illustrated in a catalogue, in the knowledge that he may produce new
product that may never display an exact reproduction of the catalogue
illustration, but which will nevertheless be regarded by the purchaser as an
acceptable expression of the catalogue illustration.
The present invention is based on the experimentally determined
discovery that if two or more differently coloured paints are applied as
discontinuous, randomly patchy deposits to a stationary target area of a
moving
substrate, or respectively to stationary target areas that are aligned in the
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direction of travel of a substrate, then, provided the long term deposition
rates, in terms
of the volume of the deposit per unit area of the substrate surface that is to
be painted, is
appropriately chosen and closely controlled, those deposits may be spread and
smoothed
to form a continuous coat of desired thickness covering a larger area of the
substrate
5 surface and displaying a familial, non-modular striated pattern.
Surprisingly, even if the
paints are similar in composition and are readily miscible, it has been found
that the
respective colours remain visible as distinct colours in the continuous coat.
Furthermore, the experiments leading to the present invention have shown that
if
the individual long term deposition rates of the component deposits and the
positioning
of the target area or areas for each component deposit are reproduced from one
operation
to another, then the non-modular pattern resulting from each operation will
display an
unchanging family resemblance. On the other hand, if any one or more of those
deposition parameters is changed, the resultant continuous coat will be
discerned as
belonging to another family.
As of now, the particular family characteristics of any selection of those
parameters cannot be readily forecast in advance, and it is necessary to trial
any
particular selection to determine whether it will produce a pleasing result.
However
experiments have conclusively demonstrated that the family character of any
selection
will be reproduced by the same selection on each different occasion.
According to an aspect of the present invention, there is provided a method of
continuously producing a continuous paint coat of substantially constant, pre-
determined
thickness, and displaying a plural colour, familial, non-modular pattern, on a
surface of a
moving substrate, comprising the steps of depositing at least two
discontinuous,
randomly patchy, differently coloured, component paint deposits, at a
predetermined,
constant, long term deposition rate for each component deposit in terms of the
volume of
paint per unit area of the surface, within a stationary target area of the
surface and
thereafter spreading and smoothing the component paint deposits carried by the
substrate
from the target area, to form the continuous coat having a familial, non-
modular pattern.
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According to another aspect of the present invention, there is provided a
method
of continuously producing a continuous paint coat of substantially constant,
pre-
determined thickness, and displaying a plural colour, familial, non-modular
pattern, on a
surface of a moving substrate, comprising the steps of depositing at least two
discontinuous, randomly patchy, differently coloured, component paint
deposits, at a
predetermined, constant, long term deposition rate for each component deposit
in terms
of the volume of paint per unit area of the surface, within stationary target
areas of the
surface respectively associated with the component deposits and at least
partly aligned in
the direction of movement of the substrate, and thereafter spreading and
smoothing the
component paint deposits carried by the substrate from the target areas, to
form the
continuous coat having a familial, non-modular pattern.
According to another aspect of the present invention, there is provided a
method
of painting at least a part of a side face of a moving substrate strip
utilising a paint
composition having a glass transition temperature, comprising the steps of pre-
heating
the strip to a pre-heat temperature above said glass transition temperature,
moving the
pre-heated strip at a pre-determined strip speed, driving a solid block of the
paint
composition along an axis of the block at a pre-determined block speed towards
said side
face to cause a liquid deposit of said paint composition to be melted from the
block and
carried away from the block on said face, spreading and smoothing the carried
away
liquid deposit, and thereafter allowing or causing the smoothed liquid deposit
to solidify,
wherein in that said block comprises at least two differently coloured
components, in that
the pre-heat temperature is above the glass transition temperatures of all of
the
components, in that the block speed is so low as to ensure that the carried
away deposit is
a discontinuous patchy deposit, and in that the spreading and smoothing
converts the
discontinuous patchy deposit into a continuous coat displaying a familial, non-
modular
colour pattern.
According to a further aspect of the present invention, there is provided a
method
of painting at least a part of a side face of a moving substrate strip
utilising a paint
composition having a glass transition temperature, comprising the steps of pre-
heating
the strip to a pre-heat temperature above said glass transition temperature,
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moving the pre-heated strip at a pre-determined strip speed, driving a solid
block of the
paint composition along an axis of the block at a pre-determined block speed
towards
said side face to cause a liquid deposit of said paint composition to be
melted from the
block and carried away from the block on said face, spreading and smoothing
the carried
away liquid deposit, and thereafter allowing or causing the smoothed liquid
deposit to
solidify, wherein at least one further block at least partly differing in
colour from the first
mentioned block and in at least partial alignment with the first mentioned
block in the
direction of strip travel is likewise driven towards the side face at a second
pre-
determined block speed, in that each block speed is so low as to ensure that
each of the
carried away deposits is a discontinuous patchy deposit, and in that the
spreading and
smoothing converts all of the carried away deposits into a continuous coat
displaying a
familial, non-modular colour pattern.
As the component deposits are discontinuous and patchy their instantaneous
deposition rates are constantly varying, thus the term "long term deposition
rate" is used
herein to indicate the average rate when taken over an area of the substrate
surface large
enough to ensure that an equivalent steady state figure is determined.
Typically, the total
volume of a component deposited on say, 0.5 to 1.0 square metres of the
substrate
surface may be regarded as the component's "long term" deposition rate.
The invention is not limited to a particular mode of deposition of the
component
deposits provided they meet the above criteria, however in preferred
embodiments of the
present invention a melt deposition process, using constant substrate speed
and
controlled block speed, of the kind described above, is used in respect of
each
component deposit.
It has been found that if the block speed is low enough, the melt deposit is
in the
form of relatively thick, randomly positioned gobbets of paint. Thus melt
deposition
using block speed control is ideal for the purposes of the present invention,
in that
notwithstanding the randomly patchy nature of the melt deposit, the long term
deposition
rate on .a constant speed substrate is still accurately determined by the
block speed.
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interface, is accurately defined, and fully blanketed in the long term by the
deposited material. Thus, if the strip speed is constant, melt deposition
using
block speed control may provide all the above described characteristics of a
component deposit as that term is used herein, namely a randomly patchy
deposit applied to a moving substrate at an accurate long term rate, in terms
of
volume of paint deposited per unit area of the substrate surface, applied
within
a predetermined stationary target area of the substrate surface.
Therefore according to a first preferred embodiment, the invention
provides a method of painting at Least a part of a side face of a moving
substrate strip utilising a paint composition having a glass transition
temperature,
of the kind comprising the steps of pre-heating the strip to a pre-heat
temperature above said glass transition temperature, moving the pre-heated
strip
at a pre-determined strip speed, driving a solid block of the paint
composition
along an axis of the block at a pre-determined block speed towards said side
face to cause a liquid deposit of said paint composition to be melted from the
block and carried away from the block on said face, spreading and smoothing
the carried away liquid deposit, and thereafter allowing or causing the
smoothed
liquid deposit to solidify, characterised in that said block comprises at
least two
differently coloured components, in that the pre-heat temperature is above the
glass transition temperatures of all of the components, in that the block
speed
is so low as to ensure that the carried away deposit is a discontinuous patchy
deposit, and in that the spreading and smoothing converts the discontinuous
patchy deposit into a continuous coat displaying a familial, non-modular
colour
pattern.
According to a second preferred embodiment the invention provides a
method of painting at least a part of a side face of a moving substrate strip
utilising a paint composition having a glass transition temperature, of the
kind
comprising the steps of pre-heating the strip to a pre-heat temperature above
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said glass transition temperature, moving the pre-heated strip at a pre-
determined strip speed, driving a solid block of the paint composition along
an
axis of the block at a pre-determined block speed towards said side face to
cause a liquid deposit of said paint composition to be melted from the block
and
carried away from the block on said face, spreading and smoothing the carried
away liquid deposit, and thereafter allowing or causing the smoothed liquid
deposit to solidify, characterised in that at least one further said block at
least
partly differing in colour from the first mentioned block and in at least
partial
alignment with the first mentioned block in the direction of strip travel is
likewise driven towards the side face at a second pre-determined block speed,
which may or may not differ from the first mentioned block speed, in that each
block speed is so low as to ensure that each of the carried away deposits is a
discontinuous patchy deposit, and in that the spreading and smoothing converts
all of the carried away deposits into a continuous coat displaying a familial,
non-modular colour pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
By way of example, several embodiments of the above described
invention are described in more detail hereinafter with reference to the
accompanying drawings.
Figure 1 is a diagrammatic front elevation of a painting station suitable
for effecting methods according to the said first preferred embodiment of the
invention.
Figure 2 is a diagrammatic sectional elevation taken on line A-A of
figure 1.
Figure 3 is a view similar to figure 1 of a painting station suitable for
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effecting methods according to said second preferred embodiment of the
invention.
Figure 4 is a diagrammatic sectional elevation taken on line A-A of
figure 3.
Figure 5 is a perspective view of a two component paint block useable
in methods according to said first or second preferred embodiments of the
invention.
Figures 6(a) to 6(e) are diagrammatic front elevations of sets of three,
two component paint blocks useable in methods according to said first or
second
preferred embodiments of the invention.
Figures 7 to 13 respectively are black and white depictions of familial,
nan-modular patterns on painted steel strip produced by exemplary
embodiments of the invention.
BEST MODE OF CARRYING OUT THE INVENTION
The apparatus illustrated by figure 1 and 2, except for the nature of paint
blocks 23 therein, is an essentially conventional melt deposition station, and
need not be described in detail herein. It may be included as a component of
a continuous paint line in a steel strip finishing mill. It comprises a steel
back-
up roll 21, a spreading and smoothing roll 22 with an elastomeric outer
cylindrical surface layer and three paint blocks 23. Each paint block 23
comprises two or more component paint compositions of differing colours, as
is described more fully below.
A steel strip 24 which is to be painted moves vertically upwardly towards
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the roll 21, turns through approximately 90 degrees as it passes over that
roll
and leaves the station more or less horizontally, having been passed through
the
nip of rolls 21 and 22. Both rolls are power driven and their surface speeds
are
not necessarily the same. The back-up roll 21 is preferably driven so that its
5 surface speed is substantially the same as that of the strip 24, and that
part of
the roll touching the strip moves in the same direction as the strip. On the
other
hand the surface speed of the spreading and smoothing roll 22 may range
between a slow speed in the opposite direction to the movement of the strip,
through zero up to about 25% of the speed of the strip in the same direction
as
10 the movement of the strip. The speed of the strip 24 is kept constant and
the
paint blocks 23 are driven towards the strip by any appropriate speed
controllable block feed device, for example, an endless belt conveyor carrying
the blocks.
Before reaching the melt deposition station, the strip 24 is cleaned and
otherwise readied to receive a paint coat. It is pre-heated to a temperature
in
excess of the glass transition temperatures of the component compositions of
the
blocks 23. Thus, paint composition is melted from the blocks 23 and deposited
on the strip at a long term deposition rate determined by the block speed, and
is carried by the strip to and through the nip of the two rolls 21 and 22.
In accordance with the invention, the block speed is so low as to ensure
that the carried away melt deposit is a discontinuous patchy deposit, and a
pressure is maintained between the rolls 21 and 22 that is sufficient to
spread
that melt deposit into a smooth, continuous coat of desired thickness
preferably
covering the side of the strip.
Also in accordance with the invention, each of the blocks 23 comprises
at least two, unblended differently coloured components, and this,
surprisingly,
results in the continuous coat displaying a familial, non-modular pattern, in
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which, it has been found, the family resemblance is uniquely determined, in
each instance, by the relative proportions and dispositions of the components
in
the blocks.
For example, if each of the blocks 23 is a marbled block, such as
illustrated by Figure 5, wherein there is 17 parts by weight of the darker
component to 13 parts by weight of the lighter component, a pattern
exemplified
by the sample length thereof shown by Figure 7 is produced. The block of
figure 5 is randomly marbled, it may be produced by placing appropriate
quantities of large fragments of the solid components in a mould, and warming
the mould and its contents sufficiently to cause the components to coalesce
without mixing. The volume proportions of the components of the block may
be selected as needed to produce different continuous coating patterns.
In other examples, a non-random arrangement of the block components
may be obtained, for example by simultaneous extrusion of the warm
components through a mufti-orifice die, or mufti nozzle extruder. Several such
blocks, each of two components, are shown in figures 6(a) to 6(e)
respectively.
It will be apparent that each of the mufti component blocks illustrated by
Figures 6(a) to 6(e) may be made as a unit, but alternatively the respective
single coloured components may be laid up, one upon or beside the other, on
a block feed conveyor to obtain the same effect. In this regard it should be
borne in mind that the blocks are naturally adhesive to an extent enabling the
laid up components to function as a single, plural coloured block.
It should be emphasised that the illustrated blocks are merely exemplary
and there is an almost unlimited variety of similar blocks of two or more
components, that could be used. All of the illustrated blocks, except for that
of
Fig. 6(c), show substantially equal volumes of each component in the finished
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block, but the actual proportions that may be used in any instance are purely
a
matter of choice, and determine the nature of the familial, non-modular
pattern
ultimately produced.
Again by way of example, reference is made to Figures 8 and 9, which
demonstrate the dependency of the family resemblance of the finished pattern
on the arrangement of the block components. Figure 8 shows a sample pattern
obtained when the blocks 23 conform with blocks 6(a) and when the lighter
coloured layers of the blocks are the lower layers as the blocks are presented
to
the upwardly moving strip, whereas Figure 9 shows the pattern produced by the
same blocks when the lighter coloured layers are the upper layers. Somewhat
surprisingly, the layer that is first met by the strip is dominant in the
finished
pattern, whereas one would intuit that the second met layer would dominate, as
at times it would presumably be deposited on top of a patch of the first met
layer.
Figures 3 and 4 show apparatus suitable for said second preferred
embodiments of the invention. It differs from the Figures 1 and 2 apparatus
only in that two independently controllable block feed devices are provided,
for
two sets of blocks 23(a) and 23(b) instead of the single feed device of the
earlier described apparatus. Thus corresponding reference numerals are used in
Figures 3 and 4 for corresponding parts in Figures 1 and 2, and they are not
further described. This embodiment provides for more flexibility of operation,
in that the deposition rate for each set of blocks may be selected by
selecting
the respective block speeds. Thus, in a two colour situation, if one wished
the
volume of one component deposit to be twice the volume of the other, one
could use single colour, similarly sized blocks and feed one set at twice the
speed of the other, whereas in the earlier described embodiment it would be
necessary to manufacture blocks including the two components in the requisite
proportions. Incidentally, it should be noted that the block speed directly
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determines the volume of the deposit. However, as the specific gravities of
differently coloured pigments usually differ it follows that equal speeds of
equally sized blocks will rarely produce equal masses of deposited components.
As the effect on the eye may depend to some extent on the relative masses of
pigment in the finished coating, the actual block speeds may have to be
adjusted
to suit. Therefore it is important that the sizes and weights of the blocks
and
the block speeds be recorded in any instance, to enable accurate pattern
replication to be achieved at a later date.
The effect of varying the respective block speeds and dispositions is
illustrated by figures 10 to 13.
Figure 10 shows a pattern produced when blocks 23(a) are the lighter
blocks and the block speeds were selected so that the long term deposition
rate
of the lighter blocks 23(a) was approximately 70% of that of the darker
blocks 23(b).
Figure 11 shows the pattern produced under the same conditions as for
figure 10 except that the deposition rate of the lighter blocks 23(a) was
approximately 25% that of the darker blocks 23(b).
Figure 12 shows the pattern when the lower blocks 23(a) were the darker
and the long term deposition rate of those darker blocks was approximately
140% of that of the lighter blocks 23(b). The relative masses of the
respective
colours in this case is substantially the same as it was in the figure 10
example,
but the effect on the eye is quite different.
Figure 13 shows the pattern when the lower blocks 23(a) were the darker
and had a long term deposition rate of approximately 45% of that of the
lighter
blocks 23(b).
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It will be noted that in each illustration, a row of three blocks is provided
at each melt deposition site, so that the total target area in each case
approximately spans the width of the strip. Such a span is preferred as it
facilitates satisfactory spreading of the melt deposits into a continuous
coat. It
should also be noted, however, that this use of multiple blocks in rows
(instead
of a single block providing the same or similar span) provides for another
variable in the selection of the finished pattern, in that the order of
deposition
of the components from each block of Figure 1 or each aligned pair of blocks
of Figure 3 is not necessarily the same as for the neighbouring blocks in the
row.
